Pressure gauge



Oct. 19, 1943. l; MATHER 2,332,103

PRESSURE GAUGE Filed Dec. 4, 1939 zw/mzjfizzke Patented Oct. 19, 1943 Irwin Mather, bli icago,

f assign-tr s a art-'wariiei' cbfliiifatiiin, Chicago; 111:, a eoriio= ratio'nor Virginia Application December reins-1e My invention relates :rtc; fiuidspressure measur ingz devices such .as the oil pressure gauges com-e manly-employed in ,-:automotive' vehicleszfo-r the measurement of lubricant pressure. Such pres; sure gauges-usually"employta pressure responsive means, such as the well known Bourdontube; one end'tof which is :fixedrand :in communication with the rsourceaoiv pressure 'toqbe' measured; and the. othersend: of :whichis connected to a :prese sure --indicating pointer: by; mechanical. linkagea' v One vof the long; prevalent disadvantages attending :the use @of these-meters has been theinaccuracy resulting from the lost'motion orf-slack in-the linkageconnectingtheBourdon tube-to the indicating element.v Although attempts have been .made to-xeliminate :lost motion between the jointsof the -va'rious linkages employed, by theuse of springs connect-ingtheseveral parts of the linkages; these attempts were never quite successful The stresses imposed: upon: the linkage by the springs asappliedtolinkages .prior to my inventiomtendedto .aiiect theaccuracy of the pressure indications given bys-the indicating element ur'iderrtheiinfluencepf theiBourdon tube. Furthermore,-a.plurality of springs was required in order to. remove-the-slackfrom-tall joints of the linkage: I I W Another diiiiculty; encountered with the prior art" was 1 the tendency. of Z the slack relieving springs unequally: to affect the indications of the pressure-gauge at difierent degreesrot deflection ,of vthe instrument. Forinstance, t e springs as usually, disposed oppose the pull of the rBourdonztube withless force at slightdefiectionsxthereof than when the Bourdon: tube is deflected-tom, larger extent bytheea-pplieation One oijthe objects of my vinventionlis toprovide:-a;.pres'sure gauge of extremely simple and economical construction but'more accurate than has hitherto xbeenz thought possible.

Anothertobject of my invention is to eliminate lostlmotion. in=:. the.- mechanical link-ages of pres- Another object 20f:- my: inventionis to provide means-for; taking ,up-the slack-in the mechanical movements, of. pressure gauges by means exertingtan equalor substantially equal compensating effect :over, the entire range of the instrument.

4, weasel-n1martinis V principle-0f -operationof the Bou flatter or-of larger eliainetera ;sure measurement cording tomy; inventionq-with a-portion of the;

dial broken away to show the underlying mechanicalstruotureof the-instrument; j p

Fig: 2 is aside-elevation" of a; pressure gauge according"to my, invention; looking along the lines'2= 2otFig;1';' H I p V t Fig: '3 'is: a;sectional View of 31 -pressure gauge according lto-c-my'sinvention along =the=line-3-3 er i 2",: 1 v

Fig; 4 is a bottonrplanview-of a pressuregauge; .takenialongathe lines fi -4 of Fig,- lpand- Fig:5 is afragmentaryiaeeview of a pressure g'aug'eembodying an alternative arrangement of mysinvention; v c In tall of" the-figi1res like-reference numerals refertto'simil'arparts; p p p I I A-ipressure .gaugeembodying invention consist :of savthreadednipple H3; provided th flanges"! 2; which support ,thebody t theinstrumentiand which are useful for mpunting the-instruments upon: a vehicle dashboard or; other supporting structure. The nipple g I 0 ispro id? with a bore M for conveying the fluid whois pressureis to be measured; The are; t nmnicates wit-h a: ei-rmilagrv Bour'don tube flat cro'ss 'section one'enei of whighgtube i I ably mounted 'upon a bracket; lil by means or solder or by welding it -.to;;the braqket. The zde'pending flange -19 of bracket its tened to' the flange i2-of -nipple;- Iii at heightithat the :"endof; the Bour M mounted upon .thebr-aeket it} is al -ignedwith He boreof-nipplelliir. A smallqap ertur'e 2T edge: of the'Bourdon tube ;is aligned joint between the-boreand the aperture delfdr fluid-tight by the judiciousdisiio'ssame time; .to helpiuiasten-the Eour'don it ulo The Bourdont b i't is a iati short (if a 66incl'o'sedxsagainst less of -lthet pres r e-p fluid by means of a smallquantit of solde applied totthe nipple; I 0, i lay this is a-rwell known expedient inlth an of Bracket i 18 bears uglw wsiuiy ran ed; i he se; 1 calibrated dial 21 is mounted by means of iii'r'ts 28. The flange 25 mounts a bushing 30 in which is journaled a pivot 3| carrying an indicator needle 29 on one end thereof. The other end of the pivot 3| carries a generally U shaped crank 32. This crank is actuated by a link 35 joining one arm 34 of the said crank 32 to 2. lug 31 of bracket 35 mounted upon the free end of the Bourdon tube It. Link 35 may consist of a light piece of wire provided with appropriate hooks 38 and 38a for engaging suitable holes 39 and 39a, ree v y. i the g 31 and the pivot crank 32, respectively. Lightness is a desirable characteristic of the link and of all of the moving parts of the instrument assembly. Consequently, the design must be of the utmost simplicity.

There must always be a certain amount of slack or lost motion in the instrument movement, because the link 35 must be somewhat loosely attached to crank 32 and lug 31 to allow free movement without the use of lubricants. This slack is very objectionable because it is greatly magnifled before being transmitted to the indicating needle 29, which therefore suffers from a large amount of play.

It has been attempted'to overcome this lost motion by the use of a coil or spiral spring reacting against the pivot in a direction opposed to its rotation under the influence of the pressure responsive element. The disadvantage of this arrangement lies in the different influence of the spring upon the instrument at high and low readings. At low readings the coiled spring that has been used in previous constructions will be under greater tension than at high readings, because at high readings the coil has partially unwound. Consequently, an unequal compensating effect is exerted upon the movement of the instrument, necessitating a specially calibrated dial. Such an unequal compensating effect practically offsets the advantage of overcoming the slack in the instrument, because the chief advantage accruing from the use of an expensive Bourdon tube is its very valuable property of giving indications, that is, deflections, entirely proportional to the pressure applied, at least for reasonable ranges of pressure. Consequently, a dial having equal divisions requiring no prior calibration may be used with the instrument. The addition of the conventional compensating spring negatives these advantages.

I have provided my pressure gauge with means for taking up lost motion in the movement which, nevertheless, does not affect the accuracy of the instrument. This means consists of a delicate leaf spring or a short piece of spring wire 45 suitably fastened by welding or by a small quantity of solder 41 to the bracket 36 or to theend of the Bourdon tube I6. The free end of the spring 45 is slightly deflected in order resiliently to stress it, and reacts against the U shaped crank 32 in a direction opposed to the pull due to the Bourdon tube [6. I wish to stress the importance of mounting the spring 45 upon the end of the Bourdon tube so that the spring moves along with the tube, thereby avoiding any substantial unequal compensating efiect.

I am not confined to the structure of the pressure gauge described, but may embody my invention in various other forms of which Fig. 5 is an illustration. The instrument there depicted is a pressure gauge wherein the pointer moves counter-clockwise with an increase of pressure,

otherwise similar to the one described previously. This necessitates the use of a spring 45 tensioned and disposed in a, slightly different manner. As will be seen from Fig. 5, the spring exerts an upward pressure as well as being upwardly curved in order to stress the instrument movement in a direction opposed. to the force due to the Bourdon tube I6.

I am enabled to apply my novel means for improving the accuracy of operation of indicating instruments to others than those described, and I therefore wish to be limited only by the following claims:

' 1. A pressure gauge comprising a threaded nipple, a bracket mounted thereupon, a pivot bearing carried by said bracket, a pivot carried by said bearing and provided with an indicator needle on one end portion thereof, a U shaped crank carried upon the other end portion of said pivot,

' a C shaped Bourdon tube one end of which is affixed to-said nipple and in communication with the bore thereof, a link joining the free end of said Bourdon tube and one arm of said crank, and a resilient wire or leaf spring carried by the free end of said Bourdon tube, and reacting against the crook of said U shaped crank in a direction opposed to motion under the influence of said Bourdon tube.

2. A pressure gauge comprising a nipple, a pointer movably mounted on said nipple, a Bourdon tube having one end communicating with said nipple and having a second free end, a link connected to the free end of said Bourdon tube, crank means connecting said pointer with said link for operating said pointer upon movement of the free end of said Bourdon tube, and a leaf spring having one end connected to the free end of said Bourdon tube and having its opposite end freely engaging said crank and exerting a substantially uniform force thereon in opposition to the force exerted through said link.

3. A pressure gauge comprising means responsive to fiuid pressure, visual indicating means operated thereby, resilient means comprising a leaf spring carried by aid pressure responsive means and exerting a force opposed to the movement of said indicating means under the influence of said pressure responsive means, a mechanical linkage connecting said indicating means and said fluid pressure responsive means, a sliding connection between said resilient means and said mechanical linkage whereby the point of contact between said resilient means and said linkage shifts lengthwise of said resilient means to vary the effective length of said resilient means and to exert a substantially uniform force on said mechanical linkage in opposition to the force exerted by the fluid pressure responsive means throughout the entire range of deflection.

4. A pressure gauge comprising a fixed bracket, a Bourdon tube mounted thereon at one end, a pivoted pointer mounted upon said bracket, a crank actuating said pointer, a link connecting the free end of the Bourdon tube to said'crank, resilient means comprising a leaf spring connected to the free end of said Bourdon tube and opposing movement of said pointer under the influence of said Bourdon tube, and a variable driving connection between said resilient means and said crank, said variable driving connection shifting with difierent positions of said tube to provide a substantially uniform force exerted on said crank by said resilient means.

IRWIN E. MATHE R, 

